Re: [PATCH V2] tracing: Fix potential double free in create_var_ref()

[Steven Rostedt <rostedt@goodmis.org>]

On Mon, 25 Apr 2022 06:37:38 +0000
Keita Suzuki <keitasuzuki.park@sslab.ics.keio.ac.jp> wrote:

FYI, always send a new version of a patch as a separate thread, never as a
reply-to of a previous version. That breaks tools like patchwork which will
not show this version of the patch.

> In create_var_ref(), init_var_ref() is called to initialize the fields
> of variable ref_field, which is allocated in the previous function call
> to create_hist_field(). Function init_var_ref() allocates the
> corresponding fields such as ref_field->system, but frees these fields
> when the function encounters an error. The caller later calls
> destroy_hist_field() to conduct error handling, which frees the fields
> and the variable itself. This results in double free of the fields which
> are already freed in the previous function.
> 
> Fix this by storing NULL to the corresponding fields when they are freed
> in init_var_ref().
> 
> Fixes: 067fe038e70f ("tracing: Add variable reference handling to hist triggers")
> CC: stable@vger.kernel.org
> Signed-off-by: Keita Suzuki <keitasuzuki.park@sslab.ics.keio.ac.jp>
> Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
>  kernel/trace/trace_events_hist.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 44db5ba9cabb..a0e41906d9ce 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -2093,8 +2093,11 @@ static int init_var_ref(struct hist_field *ref_field,
>  	return err;
>   free:
>  	kfree(ref_field->system);
> +	ref_field->system = NULL;
>  	kfree(ref_field->event_name);
> +	ref_field->event_name = NULL;
>  	kfree(ref_field->name);
> +	ref_field->name = NULL;

Nit, but it would look nicer as:

	kfree(ref_field->system);
	kfree(ref_field->event_name);
	kfree(ref_field->name);

	ref_field->system = NULL;
	ref_field->event_name = NULL;
	ref_field->name = NULL;


-- Steve

>  
>  	goto out;
>  }